To take out the blade and arm, unscrew the retaining nut and prise out the blade and arm around the pivot shaft which is serrated so that you can adjust the wiper pattern on the glass. To position the arms back into the correct park position, switch the wiper on and have the motor cycle three or four times, then switch off the wiper switch without switching on the ignition key to switch off the wiper motor. Such a move will position the wiper shafts at the appropriate park position. Lastly, the blade and arm should be carefully fitted in place on the shaft and held by the retaining nut and the blades and arms must be aligned.